version: fix ill-formed User-Agent header (#8796)

resolve: https://github.com/open-policy-agent/opa/issues/8792

I added a note in the Changelog that should hopefully be enough?

---------

Signed-off-by: Sebastian Spaink <sebastianspaink@gmail.com>

CHANGELOG.md

@@ -5,6 +5,13 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Breaking: Fix User-Agent according to RFC9110
+> OPA's outbound HTTP requests (bundle, discovery, decision log, status, `http.send`, AWS KMS/ECR)
+> previously sent `User-Agent: Open Policy Agent/<version> (<os>, <arch>)`, which is not a valid
+> RFC 9110 `User-Agent` value because the `product` token cannot contain spaces. The header is now
+> `Open-Policy-Agent/<version> (<os>, <arch>)`. Server-side log filters or WAF rules that
+> exact-match the old string will need to be updated.
+
 ## 1.17.1
 
 This release uses the latest version of Go (1.26.4) to build OPA, fixing stdlib vulnerabilities in

internal/version/version.go

@@ -33,4 +33,4 @@ func Write(ctx context.Context, store storage.Store, txn storage.Transaction) er
 }
 
 // UserAgent defines the current OPA instances User-Agent default header value.
-var UserAgent = fmt.Sprintf("Open Policy Agent/%s (%s, %s)", version.Version, runtime.GOOS, runtime.GOARCH)
+var UserAgent = fmt.Sprintf("Open-Policy-Agent/%s (%s, %s)", version.Version, runtime.GOOS, runtime.GOARCH)